Interpretive Summary: A potential source of pathogenic bacteria in ground beef is the lymphatic system, specifically the lymph nodes. There are several reports of bacteria isolated from the lymph nodes of cattle at slaughter; however, most of the studies have dealt with mesenteric lymph nodes that are not normally incorporated into ground beef. The objective of the current study was to determine the prevalence and antibiotic-resistance status of Salmonella in cattle lymph nodes associated with lean and fat trimmings that might be utilized in ground beef production. Bovine lymph nodes were collected from commercial beef processing plants. Half of the lymph nodes sampled were obtained from cull cow and bull processing plants, while the remainder were obtained from fed beef processing plants. Lymph nodes located in chuck and flank trimmings were collected for this study. Salmonella prevalence in the lymph node samples was low with an overall prevalence of 1.6%. Lymph nodes from cull cattle carcasses had a higher prevalence of Salmonella as compared to those from fed cattle carcasses. Lymph nodes from the flanks of cows/bull carcasses had the highest prevalence at 3.86%; while lymph nodes from the chuck of fed cattle carcasses had the lowest prevalence at 0.35%. Three (all from cows/bulls) of the 18 Salmonella-positive lymph node samples contained multidrug-resistant Salmonella.

Technical Abstract:
A potential source of pathogenic bacteria in ground beef is the lymphatic system, specifically the lymph nodes. There are several reports of bacteria isolated from the lymph nodes of cattle at slaughter; however, most of the studies have dealt with mesenteric lymph nodes that are not normally incorporated into ground beef. The objective of the current study was to determine the prevalence and multidrug-resistance status of Salmonella in bovine lymph nodes associated with lean and fat trimmings that might be utilized in ground beef production. Bovine lymph nodes (n = 1140) were collected from commercial beef processing plants. Half of the lymph nodes sampled were obtained from cull cow and bull processing plants, while the remainder was obtained from fed beef processing plants. Lymph nodes located in chuck and flank adipose were collected for this study. Salmonella prevalence in the lymph node samples was low with an overall prevalence of 1.6% and a 95% confidence interval (95% CI) of 0.85 to 2.3%. Lymph nodes from cull cattle carcasses had a higher prevalence of Salmonella as compared to those from fed cattle carcasses. Lymph nodes from the flanks of cows/bull carcasses had the highest prevalence at 3.86%; while lymph nodes from the chuck of fed cattle carcasses had the lowest prevalence at 0.35%. Three (all from cows/bulls) of the 18 Salmonella-positive lymph node samples contained multidrug-resistant Salmonella.